This week Matthew Norman heads to David Cameron's gastropub of choice in
Oxfordshire, The Swan, owned by the Duchess of Devonshire.

The pub landlady was an absentee when we went to The Swan, but she may be excused for playing hookey. For one thing, she turns 92 next month, and lives far away in Derbyshire. For another, you’d hardly expect to find the Dowager Duchess of Devonshire – Deborah Mitford as long ago was, Debo to her pals as is – pulling pints like Bet Lynch, or screeching, “Right, thassit, get aht of my boozer. I said, AHT!” in the dulcets of the Queen Vic’s Peggy Mitchell.

For all that, the youngest and last surviving Mitford girl and former chatelaine of Chatsworth is a major presence in this inn – an inn so picturesque, with its wisteria-clad stone frontage that a Downton Abbey scene was shot outside the door.

This, as someone clever noted, is Britain’s unlikeliest theme pub. In each of its low-beamed rooms and in a new conservatory, the walls are bedecked with sepia snaps of the Mitford sisters, and lone brother Tom, during their famously miserable childhood here. Here in the village, that is: not here in the pub.

I, and the Cotswold-dwelling friend who joined me had heard mixed reports in the few years since the Duchess installed a youngish couple as her tenants. One account raved about both food and the rooms, praising the staff’s sweetness when her adolescent son regurgitated several vodkas on the bedroom floor. Others berated it for snotty service. Much as with Unity and Herr Hitler, however, I can only speak as I find; and I found this as good a gastropub meal as any in a long while.

Mitford snaps aside, the décor is exactly what you would expect in the part of rural Oxfordshire now known as Cameron Country (Sam’n’Dave are regulars): rickety furniture, log fires, antique lights and floorboards, a gentle off-white colour scheme. If it borders on shabby, that’s how them, as we call the quality, prefers it.

As for the à la carte menu, this follows the iron rule I’ve just invented, that any cuisine be closely matched to its environment. It always irritates to find a menu in a 16th-century inn such as this giving lazy nods to the Med and the Orient, purely because that is what the current edition of the Compleat Guide to Modish Culinary Cliché dictates. Chef Richard Burkett, an alumnus of the nearby and magnificent Sir Charles Napier, sticks to the locally sourced, the poncery-free and the traditional. Hurrah for that.

My friend, not a woman lightly given to being pleased, had initial reservations. She was irked by the weeny Diet Coke bottles, her wobbly chair (“too posh for comfort, I suppose”), and the ersatz canvasses on which Debo, Unity, Diana and co appear. “I don’t like the photographs,” she observed with a certain neo-Mitfordian hauteur, “but if they must show them, at least put them in proper frames.”

Thankfully, she was assuaged by a cream of cauliflower soup. “I’ll tell you why it’s good. It isn’t oversalted, as soup so often is. Perfectly seasoned.” It also had a fine velvety texture, though the kitchen might have broken its “no fancy foreign muck here, thank you very much”, rule by enriching the flavour with a dribble of truffle oil. I backed the winner with two crunchy balls of opinionated pig’s head, the potent taste enlivened by a tangy aioli and softened by quince jelly.

It was at this point that my friend, who would have made a more effective Soviet interrogator than George Smiley’s old enemy Karla, went to work on the Duchess’s tenant, whose floppy hair suggests a chap often mistaken for Hugh Grant by myopic Americans. Within three minutes, we knew him to be Archie Orr-Ewing, where he went to school, in which regiment he served, and that his grandfather was the minister for air in Edward Heath’s government.

Another three minutes, and he would have explained the bunny sewn to his shirt, and coughed to being the heir presumptive to a baronetcy (a detail that may or may not have endeared him to Debo). The main courses arrived, however, and more than compensated for the tantalising truncation. Both were presented with rustic plainness in white bowls, and both were excellent.

My friend liked the crispy sweetness of her belly of pork with savoy cabbage and apple sauce, though she found the olive oil-infused mash a touch bitter. My plaice came on the bone, as the Lord intended, with new potatoes. The fish was fresh and juicy, and topped with smoked salmon in a delicate, buttery chive sauce.

Archie popped back to inquire after puds, and displayed an ex-soldier’s obedience when my friend ordered him to ring her butcher. Her vanilla panna cotta was “not quite fluffy enough, but delicious”, and my sticky toffee sundae, elegantly served in a Martini glass, was predictably, life-shorteningly gorgeous.

Archie, who had taken on a shell-shocked look, was busy elsewhere now. When my friend turned to the Serbian manager, curiously asking if he was related to John Malkovich, it seemed time to request the bill. “Very, very good indeed,” she said as we left. “I’m coming back on Monday.”

She was right to be impressed. The Swan is hereby awarded not just the numeral you see above my left shoulder, but also the suitably Mitfordian rating of U.